Crude petroleum is a very complex mixture containing a wide range of hydrocarbons. It is converted into a diversity of fuels and chemicals through a variety of chemical processes in refineries. Crude petroleum is a source of transportation fuels as well as a source of raw materials for producing petrochemicals. Petrochemicals are used to make specialty chemicals such as plastics, resins, fibers, elastomers, pharmaceuticals, lubricants, and gels.
The most important transportation fuels—gasoline, diesel, and jet fuel—contain distinctively different mixtures of hydrocarbons which are tailored toward optimal engine performance. For example, gasoline comprises straight chain, branched chain, and aromatic hydrocarbons generally ranging from about 4 to 12 carbon atoms, while diesel predominantly comprises straight chain hydrocarbons ranging from about 9 to 23 carbon atoms. Diesel fuel quality is evaluated by parameters such as cetane number, kinematic viscosity, oxidative stability, and cloud point (Knothe G., Fuel Process Technol. 86:1059-1070 (2005)). These parameters, among others, are impacted by the hydrocarbon chain length as well as by the degree of branching or saturation of the hydrocarbon.
Microbially-produced fatty acid derivatives can be tailored by genetic manipulation. Metabolic engineering enables microbial strains to produce various mixtures of fatty acid derivatives, which can be optimized, for example, to meet or exceed fuel standards or other commercially relevant product specifications. Microbial strains can be engineered to produce chemicals or precursor molecules that are typically derived from petroleum. In some instances, it is desirable to mimic the product profile of an existing product, for example the product profile of an existing petroleum-derived fuel or chemical product, for efficient drop-in compatibility or substitution. Recombinant cells and methods described herein demonstrate microbial production of fatty acid derivatives with varied ratios of odd:even length chains as a means to precisely control the structure and function of, e.g., hydrocarbon-based fuels and chemicals.
There is a need for cost-effective alternatives to petroleum products that do not require exploration, extraction, transportation over long distances, or substantial refinement, and avoid the types of environmental damage associated with processing of petroleum. For similar reasons, there is a need for alternative sources of chemicals which are typically derived from petroleum. There is also a need for efficient and cost-effective methods for producing high-quality biofuels, fuel alternatives, and chemicals from renewable energy sources.
Recombinant microbial cells engineered to produce fatty acid precursor molecules having desired chain lengths (such as, chains having odd numbers of carbons), and fatty acid derivatives made therefrom, methods using these recombinant microbial cells to produce compositions comprising fatty acid derivatives having desired acyl chain lengths and desired ratios of odd:even length chains, and compositions produced by these methods, address these needs.